The classification criteria are the principles by which classification categories are aggregated to form broader or higher-level categories in the classification structure. Three classification criteria are used in the ASCRG to form the categories of the classification:

similar religious beliefs;

similar religious practices; and/or

cultural heritage.

Religious Groups are combined to form the Narrow Groups (middle level) of the classification on the basis of their similarity in terms of these criteria. Although the Religious Groups are not necessarily identical in any particular characteristics, the Narrow Groups formed are relatively homogeneous in terms of the set of classification criteria.

The Broad Groups were developed in a slightly different manner. On the basis of the number of adherents, worldwide, the major world religions are generally accepted as: Christian, Muslim, Hindu, Buddhist, Tao, Confucian, Tribal, Animist, and Jewish. It would seem appropriate to designate these major religions as Broad Groups in the classification, particularly as they are broadly homogeneous in terms of the classification criteria (beliefs, practices, and cultural heritage). However, consideration of the number of adherents of each of these religions (in Australia) indicates that it is unacceptable in terms of the statistical balance of the classification to include Tao, Confucian, Tribal and Animist religions as Broad Groups. Furthermore, the usefulness and acceptability of the classification would be impaired by such a decision.

Thus, on the basis of a broad application of all the classification criteria, supported by the size of the religions in Australia, Buddhism, Christianity, Hinduism, Islam and Judaism comprise Broad Groups within the classification. This application of the criteria enables the delineation of appropriate Narrow Groups (constructed on the basis of a more rigorous application of the criteria) as subsets (sub-categories) of these major groups. The classification criteria are then applied so that other major world religions and residual Narrow Groups form a meaningful and useful classification structure within a residual Broad Group: Other Religions.

The structure can legitimately be described in conventional terms: Religious Groups (base-level units) grouped to form Narrow Groups on the basis of similarity in terms of the classification criteria; Narrow Groups grouped to form Broad Groups on the basis of a broader similarity in terms of the classification criteria.

A further Broad Group (No Religion) has been included in the classification for practical reasons and to make the classification more useful (see: Scope of the classification). Because this group consists of entities not considered to be Religious Groups it was, obviously, not developed in accordance with the classification criteria.